1. Field of the Invention
The present invention relates to a lithium secondary battery anode member for realizing high capacity and high safety, and a method for manufacturing the same.
2. Description of the Background Art
Highly integrated, high-performance devices such as large-scale integrated circuits have been recently put into practical use due to significant development in microelectronics, particularly technology for manufacturing semiconductor devices. By using such integrated high-performance devices in control systems of various apparatuses, these apparatuses can be rapidly decreased in size, thereby contributing to miniaturization and multifunctionalization not only in various industrial fields but also in the field of general home electric appliances.
These electronic devices are generally made cordless, i.e., they include self-sustained power supplies and tend to become operable without relying on commercial power supplies. As a power supply, a primary or secondary battery is generally used. In order to decrease the overall size and weight of an apparatus and permit the operation of the apparatus for a long period of time, development of a high-performance battery is required.
In particular, in order to realize a small lightweight battery, a lithium battery using lithium in oxidation-reduction reaction is suitable. As a lithium battery, development of a secondary battery which can be repeatedly used many times by electric charging is demanded.
In particular, various attempts have been made to improve the performance of solid electrolytes used for lithium batteries. For example, Japanese Unexamined Patent Application Publication No. 2004-220906 discloses a technique in which a lithium secondary battery anode member is formed by laminating a lithium metal film and a solid electrolyte film on a substrate, and the solid electrolyte includes lithium, phosphorus, sulfur, and oxygen as main components.
Japanese Patent No. 3407733 discloses a technique in which a solid electrolyte film containing lithium and sulfur as essential components, an element selected from phosphorus, silicon, boron, germanium, and gallium, and sulfur is heated to a temperature of 40° C. to 200° C. to increase the ionic conductivity.
Other inorganic solid electrolytes having lithium ionic conductivity and including lithium, phosphorus, and sulfur are disclosed in Solid State Ionics, 170 (2004), pp. 173-180. The X-ray diffraction patterns of the resulting inorganic solid electrolytes are shown in FIG. 2 on page 176 of the document.
Solid electrolytes used for lithium secondary batteries are required to have characteristics, such as high lithium ionic conductivity, low electronic conductivity, and satisfactory voltage resistance. Furthermore, in relation to the formation on lithium metal, the solid electrolytes are required to have stability against lithium metal, adhesiveness at interfaces between solid electrolyte films and lithium metal, and stability against organic electrolytic solutions. In particular, when a solid electrolyte is used as a protective film for a lithium metal surface, it is necessary for the solid electrolyte not to react with lithium metal, and it is important for the solid electrolyte not to be decomposed by reduction with lithium metal.
In particular, it is important that the solid electrolyte is stable against the reducing property of an anode active material such as lithium metal or the like, reductive decomposition little occurs, and electronic conductivity is low or not increased. From the viewpoint of these requirements, the solid electrolyte film disclosed in Japanese Unexamined Patent Application Publication No. 2004-220906 contains oxygen and can inhibit short-circuit due to the occurrence of dendrite from a lithium metal anode. However, long-term durability against reaction between solid electrolytes and lithium metal has been not elucidated.